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FOOT OF UNGULATES

the limb passes through the third finger, which Is larger than any of
the others, and is symmetrical in itself. In this the present group
contrasts with the Artiodactyla, where the axis Is not " mesaxonic/'
"but where there are two digits, on either side of the axls> which are
symmetrical with each other. This arrangement of the limbs is
highly characteristic, hut appears to be not quite universal. In
the Titanotheres, which form a group of the Perissodactyles, the
\-\               fore-limbs are not quite accurately mesax-

1 •*r'            onic.    ISTor on the other hand can all Ungu-

lates which show the Perissodactyle condition
be safely included in the present group. The
ancient Oondylarthra and the Utoptema
show precisely the same state of affairs.
But other features in their organisation lead
to their separation from the Perissodactyles,
of which, however, the Condylarthra are
probably ancestors. The Utoptema on the
other hand, which possess even one-toed
members like E^iius, are believed to repre-
sent a case of parallelism in development.
The number of functional toes varies from
four to one. In the ankle joint the astra-
galus either does not, or does only to a
comparatively slight extent, articulate with
the cuboid as well as with fche navicular
FIG. 122. —Boaes of the bone. Moreover the fibula when present

mantis of Camel (Cameltis   j                ,                       ,                   ,   .           .,,        .,

f>ac£nanu$°).      x£.     c,   Q-°©s   not   as   a   rule    articulate   with,    tne

Cuneiform ;  I, lunar; m,   calcaneum.       In     the      Opposed     group      of

magnum *,  JZ,  radius ;  s,     ,    . .    ,     ,   ,         . _                .    Jrx                    «     i

floapiioid j td, trapezoici; Artiodactyles   the  precise   reverse   of  these

HowS-^i£?jr^.(fr0m conditions    obtains.      It   is   usually   stated

as   part   of   the   definition   of   this   group

that they do not possess horns of the type of those met
with in the Cervicornia and Cavicomia. But the strong bony
bosses on the skull of many Titanotheres, so curiously remin-
iscent of those of the not nearly related Dinoceras and JProto-
ceras, may weli have supported horns of the Ox. and Antelope
pattern.

The teeth of the Perissodactyles are lophodont, more rarely
The selenodoiit Artiodactyle form of molar is not
Th*i dental formula, moreover, is at least near the